1. Field of the Invention
This invention relates to a bone sealant and more particularly to a synthetic absorbable lactide/glycolide copolymer used for the control of osseous hemorrhage. (The term "lactide/glycolide copolymer" used herein, is intended to refer to the copolymer derived from lactide/glycolide monomers as starting materials.) This invention also relates to mixtures of the copolymer in a biocompatible base, and also to the process for applying the bone sealant.
2. Description of Prior Art
Various substances and compositions have been employed by members of the medical profession to control bleeding from cut bone surfaces. One class of materials used for the control of this type of hemorrhage is called bone wax. Bone waxes are used for the purpose of controlling hemorrhages from the cut surfaces of bones, such as those of the skull, by forcibly smearing the wax over the cut surface so that the material acts mechanically to occlude and seal the open ends of the bleeding osseous vessels and sinuses.
Bone waxes used in surgery today are generally prepared from refined beeswax which has been admixed with other nonabsorbable and water insoluble hydrocarbons and vegetable oils. Certain disadvantages inhere in these bone wax compositions, as for example, relatively poor adhesion properties, and the hard brittle state of the wax at room temperatures requiring use at elevated temperatures. Futhermore, paraffin based commercial bone wax is not absorbed by the body and thus remains at the site of application for long periods of time. As a result the wax acts as a foreign body, tending to make it difficult for the body to fight infection and inflammatory reactions that may be introduced in the surrounding tissue, and it also interferes with bone regrowth.
In order to overcome the latter problem, British Pat. No. 1,584,080 discloses an absorbable hemostatic bone sealant, which contains the active components collagen and fibrin. However, the composition of British Pat. No. 1,584,080 suffers from the disadvantage that its storage conditions must be controlled in order to retain desirable aesthetic and tactile properties, since biological materials of animal origin are used.
U.S. Pat. No. 3,395,217 discloses nonabsorbable bone wax compositions comprised of low molecular weight ethylene copolymer waxes containing from about 15 to about 40 percent by weight of another unsaturated consituent and having molecular weights in the range of 1000 to 4000. These waxes have a semisolid consistency such that they can be kneaded between the fingers when at room temperature and have the right amount of tack and adhesion so that they can be easily manipulated in the hands of the surgeon or applied by any suitable applicator such as a gloved finger, spatula or appropriate disposable applicator.
U.S. Pat. No. 2,722,999 describes an absorbable bone wax comprised of a water soluble innocuous base and free acid cellulose glycolic acid ether or free acid cellulose hydroxypropionic acid ether as a hemostatic agent. The composition also preferably contains a tackifier such as cellulose glycolic acid ether salt or cellulose hydroxypropionic acid ether salt (preferably sodium salt) and water as a plasticizer. It should be noted that cellulose and its derivatives are generally not biologically degradable, but merely soluble, and, if the molecular weights are high enough, may not even pass through the kidneys.
The Annals of Surgery 132, 1128 (1950) describes an absorbable hemostatic bone wax containing powdered oxidized cellulose as the hemostatic agent in a base of polyethylene glycol. The base is a mixture of high and low molecular weight polyethylene glycols selected to provide the malleability and consistency of material desired for this use. However, polyethylene glycols are completely water soluble. When they comprise the largest percentage of the mixture, the mixture becomes slimy in the area wet with tissue fluids, this being true of any water soluble base. In addition, a large percentage of polyethylene glycols give a pronounced tissue reaction.
U.S. Pat. No. 4,186,448 discloses a one-piece molded body member for filling and covering a bone void or soft tissue deficiency, which body member attracts blood in fluid suspension by capilliary action until clotting forms which ultimately leads to the formation of tissue and/or bone. The body member is made of a biodegradable material such as polylactic acid.
U.S. Pat. No. 4,137,921 discloses a relatively high molecular weight, fiber forming, copolymer of lactide and glycolide. This high molecular weight material would not be at all suitable as a bone wax.
The present invention provides a new synthetic absorbable bone sealant which is a putty-like semisolid at room temperature. The softness of the sealant allows the material to be packaged in a syringe, plastic or coated paper envelope, or aluminum or glass tube from which it may be extruded or dispensed in desired amounts during use. The sealant has sufficient tack so that it adheres to bone surfaces, yet is easily manipulated in the hands of the surgeon without crumbling or sticking to the surgeon's gloves. Considering that known lactide/glycolide copolymers are solid, hard materials it is surprising that the instant copolymer possesses the above-described putty-like properties. Furthermore, the instant copolymer also possesses the advantage of not "setting-up" even after a long period of standing, and it also maintains an aesthetic physical appearance. The instant copolymer may be sterilized by Cobalt 60 (gamma irradiation), avoiding tedious heating to high temperatures.
It is to be noted that polymers derived from lactide/glycolide (such as the instant copolymers) have a good history of in vivo absorption due to hydrolysis of ester bonds, have shown minimum tissue reaction and are nontoxic (lactic and glycolic acids are both body metabolites). See U.S. Pat. No. 3,636,956.